January Temperatures Predict Tobacco Blue Mold Severity: Evidence for Local Source and Long-Distance Transport of Inoculum in Connecticut.

The tobacco blue mold pathogen, Peronospora tabacina, has been periodically reintroduced to the Connecticut River Valley cigar wrapper tobacco (Nicotiana tabacum) area of Connecticut and Massachusetts. Once introduced, there is a greater likelihood of disease in following years. Blue mold occurred from 1937 to 1956, 1979 to 1981, and most recently from 1996 to 2008. Disease severity was evaluated and rated annually from 1979 to 2008, and was correlated (r = 0.84; P = 0.002) with January temperatures when the pathogen was present in moderate amounts the previous year (severity rating >1). The date of the first report of disease was negatively correlated with disease severity the previous year (r = -0.63) and February temperatures (r = -0.83). Blue mold severity was not correlated with the date of the first disease, the previous year's disease severity, or rainfall amount or frequency after introduction of the pathogen. January temperatures may be used to predict the need for early-season fungicide applications to control disease from local overwintering inoculum following moderate to high blue mold severity. In years following little or no disease, forecasts of long-distance transport will continue to be a valuable tool to predict the risk of long-distance reintroduction and the need for fungicide application based on exposure.